The use of composts has been known for years as a sensible, environmentally safe and efficient method for converting organic waste such as fallen leaves, grass clippings and wet garbage into useful fertilizer or ground filler. Aerobic decomposition or composting is the controlled decomposition of organic matter in the presence of atmospheric oxygen through natural microbial activities. Since the decomposition of organic matter is dependent upon the microbial activity it is desirable to create an environment in which the microbes can thrive. For example, it is preferable to provide the proper oxygen, moisture, and temperature conditions that will promote the biological activities of microbes and, therefore, speed up the decomposition process of the organic matter.
In a typical compost, naturally occurring microorganisms digest the organic waste converting it into water, carbon dioxide, nitrogen, potassium (K.sub.2 O), phosphorus (P.sub.2 O.sub.5) and lower molecular weight hydrocarbons. Optimum conditions for this degradation process typically comprise temperatures of about 40.degree.-60.degree. C. and moisture levels of about 40-60%. The heat necessary to maintain these optimum conditions is generated by the microorganisms as they digest the waste material.
Those skilled in the art will also appreciate that composting generally requires a minimal amount of maintenance. Such maintenance may include the "turning" of the compost to resupply oxygen to the internal portions of the compost thereby replenishing oxygen which is depleted by the microorganisms as they digest the waste material. Oxygen is essential to the respiration of bacteria and fungi that decompose the waste. The presence of adequate oxygen will promote the growth of these microbes and prevent the process from becoming anaerobic or oxygen deprived. The lack of atmospheric oxygen can decrease the rate of decomposition and promote the production of foul odors.
As one way of reducing solid wastes, it is not uncommon for government entities to establish large composts with the leaves and grass clippings generated by their populations. In order to effectively conduct large-scale compost programs, manageable containers, e.g. bags, should be supplied to community residents so that the leaves and grass clippings can be properly bagged for transportation to a compost site.
One type of compost bags which has gained some approval by municipalities are made of multi-wall craft paper. While these paper bags have a good rate of degradation, they are bulky, relatively expensive to manufacture, and tend to lose their strength when wet. While conventional polyethylene plastic bags do not have these disadvantages, steps must be taken to enhance this degradation of such bags. For example, one known method involves adding starch and a pro-oxidant such as a transition metal salt to polyethylene prior to extruding the resin into films. Adding starch to the polymer resin necessitates processing precautions, such as moderating the preparation and extrusion temperatures in order to avoid burning the starch and carbonizing the extrusion die.
Another limitation imposed on known polyethylene compost bags of this type is a limitation on the amount of transition metal salt which may be added. The transition metal salt is added in order to enhance the thermal oxidative degradation of the bag. By increasing the amount of transition metal salt in the polyethylene matrix, the temperature at which degradation occurs is lowered and thus, degradation may proceed more rapidly. In order to avoid premature degradation from the high temperatures incurred during shipping of the compost bags by trucks or when the bags are stored in a warehouse, the amount of prooxidant in conventional degradable thermoplastics is generally maintained at low levels.
Another method of avoiding premature degradation is through the use of stabilizers which inhibit the action of the prooxidant but, when consumed, will allow the degradation to proceed. Defining the precise amount of stabilizer needed to assure adequate storage stability is difficult. If too little is added, the material will degrade during storage and warehousing. If too much is added, the article will not degrade under composting conditions.
It would, therefore, be desirable to provide a compost bag in a manner which provides the strength, economy and low bulk of plastic bags while being easier to manufacture and having a more controlled rate of thermal oxidative degradation than compost bags known in the art.